<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .test-css{  color: blue; font-size: 18px;background-color: #37C7D4; }
    </style>
    <link rel="stylesheet" href="./css/test.css">
</head>
<body>

<p style="color: red;font-size: 18px;background-color: #FFF38F;">行内第1种写法</p>
<span style="color: red;font-size: 18px;background-color: #FFF38F;">行内第2种写法</span>
<span style="color: red;font-size: 18px;background-color: #FFF38F;">行内第3种写法</span>

<p class="test-css">嵌入式第1种写法</p>
<span class="test-css">嵌入式第2种写法</span>
<span class="test-css">嵌入式第3种写法</span>

<p class="test-link">外链式第1种写法</p>
<p class="test-link">外链式第2种写法</p>
<p class="test-link">外链式第3种写法</p>

<span></span>
</body>
</html>